Identification of the Superconducting Phase in the Nd-Ce-Sr-Cu-O System

Abstract

Phase search experiments were performed to identify the superconducting phase in the Nd-Ce-Sr-Cu-O system. A single phase superconductor was obtained form the nominal composition (Nd 0.66 Ce 0.135 Sr 0.205 ) 2 CuO y . It has a tetragonal cell with a =3.8558(1) and c =12.487(1) Å. From powder X-ray diffraction and electron microscopic observations, it was confirmed that the metal positions in this phase are identical to those in the K 2 NiF 4 structure but with cationic order of Nd(Ce) and Sr. Three structure models including oxygen positions are proposed and discussed. Although we could not be absolutely conclusive, the structure which consists of alternative stacking of K 2 NiF 4 - and Nd 2 CuO 4 -type slabs seems to be most likely.